It is highly desirable to have containment sumps or pans installed under the fuel dispensers at a service station to prevent accidental contamination of the soil. These dispenser "pans" can be installed during construction or retrofitted to existing operating stations. Use of a dispenser pan is very effective for containing accidental spills or leaks that may occur inside the dispenser.
A negative side effect is that the dispenser pans are also very effective containment for any water that enters the pan from the outside the dispenser, such as occurs during rain storms or dispenser cleaning. Since containment sumps that have had prior contact with gasoline is the norm, any water collected in these sumps represents a hazardous waste and is very costly to remove.
Attempts by the dispenser manufacturers have been made to make the dispenser itself watertight, thus preventing ingress of water into the containment pan. While these systems are somewhat successful, the cost of such systems is very high. It is desirable to have a low cost solution to the problem.